Such a circuit arrangement and such a method are known from the prior art, cf. in this regard FIGS. 1 to 3b which will be explained in more detail below for the purpose of introducing the problems on which the invention is based and in which:
FIG. 1 shows a circuit arrangement in which a device 10 for modifying the phase gating angle of an input voltage Ue, in particular a sinusoidal AC voltage, for example a system voltage, corresponding to a dimming input value 8 is provided at the input. Said circuit arrangement provides a voltage U1 having a modified phase gating angle at its output. The voltage U1 is fed to a rectifier circuit comprising the four diodes D1 to D4. The voltage Ug can be tapped off at a resistor Rg. The voltage Us, which is derived from the voltage Ug across a voltage divider, which comprises the resistors R1 and R2, and an averaging unit, to which the resistor R2 likewise contributes in addition to a capacitor C1, is made available as the control signal at the output of the circuit arrangement.
This control voltage is now made available to an electronic ballast (not shown) to which the lamp to be dimmed is coupled. The problems associated with this circuit are explained with reference to FIGS. 2 and 3:
FIG. 2a shows the waveform of the voltage Ug for different voltages, in particular system voltages, applied at the input of the device for modifying the phase gating angle given an identical dimming input value 8, i.e. both times for a phase gating angle φ of 20°. In FIG. 2a, the voltage Ugh corresponds to a system voltage of 277 V, and the voltage Ug1 corresponds to a system voltage of 120 V. The control voltages Ush and Us1 which correspond thereto are illustrated in FIG. 2b. It can be seen that, despite an identical dimming input value 8, the present circuit arrangement for producing a control signal for the purpose of dimming at least one lamp provides very different control voltages at the electronic ballast which is coupled to the lamp, depending on the input voltage.
FIG. 3a shows the voltage Ug for different phase angles φ, the system voltage being 120 V. The voltage Ug1 corresponds to a phase angle φ of 20°, while the voltage Ug2 corresponds to a phase angle φ of 120°. FIG. 3b shows the control voltages Us1 and Us2 corresponding thereto.
As a result, such a circuit arrangement as illustrated in FIG. 1 is not suitable for operation using different input voltages, in particular system voltages, to be applied to the device for modifying the phase gating angle since the control signal Us provided at the output of the circuit arrangement depends on the input voltage applied to the device for modifying the phase gating angle. At an input voltage of 277 V, the value range for the control voltage is approximately 1 V to 3 V, while at an input voltage of 230 V, a value range for the control voltage of approximately 0.5 V to 1.7 V results.